Production of an acid soluble, partially purified lymphokine fraction from the supernatant human lymphoblast cell line, RPMI 1788, is described. This fraction can be readily produced in large quantities and appears to be adequate for clinical studies without additional purification. It contains less than 0.1 percent of the protein in the original starting material and yields an increase of 50- to 200-fold in biological response over the starting material, depending upon the assay, with increased activity for MAF, spleen killer cells, lymphotoxin and mouse tumor inhibition. Plans for Phase I studies on cancer patients in appropriate protocols are on file under IND No. BB 1395. This proposal describes a program designed to meet the cell and supernatant production required for clinical trials, isolation, purification, and chemical characterization of the active moieties in this lymphokine fraction.